The present invention relates to improvements in the field of holography. More particularly, the invention is directed to a method of taking holographic portraits of human subjects, as well as to a photograph booth for providing a hologram of a human subject positioned inside the booth.
A hologram is an interference pattern which is produced by the interference of a reference beam with light reflected from or transmitted through an object, and which can be recorded as such on a photographic emulsion. This interference pattern on the holographic film should not move during the exposure time; otherwise, a poor or ruined hologram will result. This requires that all components of the holographic apparatus remain stationary to a fraction of a wavelength during the exposure time. Thus, when making holograms with continuous wave gas lasers, which require an exposure time of about a second, use has to be made of massive stabilized tables. Therefore, it has been impossible up till the 1970's to make holograms of objects which could not be displaced and brought to a holographic studio, as well as holograms of moving objects.
Portable holographic cameras have been designed with a view to overcoming the above drawbacks. An example of such a camera is described in U.S. Pat. No. 3,837,726 of Sept. 24, 1974. In this holographic camera, in order to be able to vary the coherent range within which the object can be placed to be recorded on the hologram, a rather complex optical system is provided for varying the optical path length of the object beam or the reference beam. The camera includes a range finder having a rotatable mirror which is rotated to determine the distance from the camera to the object. The rotatable mirror is associated with the optical system for varying the optical path length of the object beam or reference beam so that the optical path length of either beam may be varied according to the distance measured by the range finder in such a way as to make the optical path length of the reference beam equal to that of the object beam. Due to its complexity, the optical system of such a camera is thus prone to malfunction and the camera may therefore present potential hazards to persons when taking holographic portraits of human subjects.
Pulsed laser holocameras for recording action scenes, or the other hand, are known, for example from U.S. Pat. No. 3,529,883 of Sept. 22, 1970. However, the holographic camera described in this patent is essentially limited to transmitted-beam type holograms, that is, holograms made with an object beam transmitted through the object to be recorded on the hologram. Although such a holographic camera is suitable for recording transmission holograms of moving objects, the object must necessarily be transparent or translucid for permitting transmission of the object beam therethrough. Accordingly, it is impossible to take holographic portraits of human subjects.
With respect to safety, it is extremely difficult to safely apply pulse laser holography to making holograms of living people due to the intense nature of pulsed laser radiation. This is particularly true in the case of reflection holograms, where the reference beam illuminates the holographic film from the side opposite the subject. Since reference beam light transmitted through the holographic film in a direction toward the subject and may accidentally be viewed by the latter, a danger zone is created between the holographic film and the subject. In this danger zone, the energy density may be as high as 180 times the threshold for biological damage by laser radiation at the retina of the eye, and may thus cause permanent eye damage.